The pet food industry has undergone a remarkable evolution within the last few years, perhaps due largely to greater demand by competitors and an increase in specialty markets generated in response to the more knowledgeable consumer. From one aspect, the market is increasingly demanding pet foods lower in fat to compensate for lower activity levels of many modern pets. On the other hand, a very specific segment of the market is demanding a nutritious, high fat diet for specialty feed, as well as for starter or younger pets. Pet foods with high fat composition are very desirable in most instances because: 1) The cost of fat is lower than most other ingredients. 2) Fats can carry a variety of flavors due to their ability to easily encapsulate the flavors. 3) Fats provide a very palatable taste to the food and can be a source of texture development. 4) For specialty feeds, aquafeed, and adolescent house pets, fat is used as a source of high energy and nutrition.
Extrusion cooking has been and is becoming a more widely and commonly used processing technique in the pet food industry, with a concomitant rapid rise in the extent of extruder sophistication and ease of operation. Improved technology, innovative processing, and the introduction of twin screw extruders into various markets opened a broad horizon for new process development, incorporating a wide variety of steps.
Use of carbonation in the food industry has been exclusively used in the area of carbonated waters. This technology has found itself to be useful in only a small part of the food industry with not much application into the pet food or feed industry. This has mainly been due to greater demand for a lower fat content in the food and the pet food industry. However, with the new developments in the specialty pet food and feed markets, more and more new niche areas have been developed, some of which are in need of very high fat and high protein content products as mentioned above. The feed industry also has gone through a shift in the fat requirements for specific feeds, some requiring as high as 50% fat or greater, with the majority of the rest of the ingredients to be made of proteins and carbohydrates. In order to achieve the fat requirements necessitated by the above markets, three process approaches have been attempted. 1) The first approach was to try to incorporate the fat within the extrusion system in order to encapsulate the fat within the proteins and carbohydrates matrix. This is limited by the type of the extruder being used in the process, as well as the extent of denaturation and gelatinization of the matrix being 8%, and the twin screw extruder can incorporate up to 18-20% unless the process is below the melting point of the fat and the fat is of a very high hydration value, in which case the extruder is used as a cold former. 2) Another approach was the encapsulation of the fat by the protein carbohydrate shell extruded at the die in the form of a tube in which the fat is co-extruded and sealed into a pillow like consistency. Thus the formed and cut piece contains fat within the structure in the form of a filled pillow. 3) The third process incorporated the use of fat sprayed onto the surface of the cut extrudate at the die or the use of a tumbler with a fat spray system application to the surface of the extrudate after it has been cooled or dried.
All of the above methods are limited in one form or another. The first two methods have a maximum incorporation of fat of less than 20%, with pellets or extrudates having a very high density, thus causing the separation of the fat from the pellets due to high density and weight of the pellets during storage and shipping. It also has a negative market view by the customer of not getting much for the price due to the high density of the end product. There is a need to incorporate the lower density extrudate with a higher fat content.